Chuck devices for holding wafers are used in film-forming equipments such as CVD equipments, sputtering equipments and the like and etching equipments for fine processing which are used in semiconductor manufacturing steps.
In the above chuck devices, a vacuum chuck system and a mechanical cramp system have so far been employed, and an electrostatic chuck (ESC) system in which a semiconductor wafer is adsorbed by virtue of an electrostatic attracting force (coulomb force) has come to be used in accordance with a rise in a degree of a semiconductor production process in recent years. The above electrostatic chuck system exerts excellent characteristics in terms of correction of a wafer flatness and soaking as compared with a vacuum chuck system and a mechanical cramp system which have so far been used. Operation characteristics of an electrostatic chuck include preferably generating a large chucking force during applying a voltage to prevent an adsorbed matter from falling and reducing immediately the chucking force when releasing the applied voltage to make it possible to readily detach the adsorbed matter.
On the other hand, steps in which halogen base corrosive gases such as a fluorine base corrosive gas, a chlorine base corrosive gas and the like and plasma thereof are used are included in a semiconductor manufacturing line of IC, LSI, VLS and the like. Among them, fluorine base gases such as CF4, SF6, HF, NF3, F2 and the like and chlorine base gases such as Cl2, SiCl4, BCl3, HCl and the like are used in steps of dry etching, plasma etching, cleaning and the like, and therefore corrosion brought about by the above corrosive gases and plasma raises a problem to constitutional members such as an electrostatic chuck and the like in a semiconductor manufacturing apparatus.
In this connection, yttrium-aluminum-garnet and matters obtained by adding oxides of rare earth elements excluding yttrium to yttrium-aluminum-garnet have so far been used as a corrosion resistant material for an electrostatic chuck (refer to, for example, a patent documents 1 to 3).
It is disclosed in the patent document 1 described above that the corrosion resistance is improved by combining yttrium aluminum composite oxides with rare earth elements excluding yttrium. This is considered to be attributable to the facts that halides of rare earth elements excluding yttrium have a pretty higher vaporization temperature than those of halides of yttrium and aluminum and that the halides produced work as a protective film on the surface to inhibit vaporization of yttrium and aluminum and reaction thereof with halogens.
The rare earth elements (RE) excluding yttrium (Y) are preferably at least one selected from lanthanum (La), neodymium (Nd), samarium (Sm), gadolinium (Gd) and dysprosium (Dy) in terms of availability and an effect of improving the corrosion resistance. It is described therein that among them, samarium (Sm) and gadolinium (Gd) have a marked effect of improving the corrosion resistance.    Patent document 1: Japanese Patent Application Laid-Open No. 315308/2004    Patent document 2: Japanese Patent Application Laid-Open No. 151559/2001    Patent document 3: Japanese Patent Application Laid-Open No. 236871/1998